US9608785B2 - Channel estimation method and apparatus using reference signal - Google Patents

Channel estimation method and apparatus using reference signal Download PDF

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US9608785B2
US9608785B2 US14/359,064 US201314359064A US9608785B2 US 9608785 B2 US9608785 B2 US 9608785B2 US 201314359064 A US201314359064 A US 201314359064A US 9608785 B2 US9608785 B2 US 9608785B2
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csi
port
crs
corresponds
data
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US20140314041A1 (en
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Hyungtae Kim
Jonghyun Park
Hanbyul Seo
Kijun KIM
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LG Electronics Inc
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LG Electronics Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0204—Channel estimation of multiple channels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0621—Feedback content
    • H04B7/0626—Channel coefficients, e.g. channel state information [CSI]

Definitions

  • a user equipment measures/estimates a downlink channel using a cell-specific reference signal (hereinafter abbreviated CRS) from a base station to generate/calculate channel state information and may demodulate data based on the channel measured/estimated using the CRS.
  • CRS cell-specific reference signal
  • CSI-RS channel state information-reference signal
  • DMRS demodulation reference signal
  • one technical task of the present invention is to provide a method of precisely and efficiently determining channel state information on a channel used for performing data demodulation.
  • Another technical task of the present invention is to provide a method for a user equipment to compensate for a difference between a channel based on the CRS and a channel based on the CSI-RS.
  • the other technical task of the present invention is to provide a method for a base station to compensate for the difference between the channel based on the CRS and the channel based on the CSI-RS.
  • a method of estimating a channel by a user equipment in a wireless communication system includes receiving a cell-specific reference signal (CRS) and a channel state information-reference signal (CSI-RS) from a base station, generating CSI on a channel estimated using the CRS based on CSI on a channel estimated using the CSI-RS and a mapping relation between a CRS port and a CSI-RS port, reporting the generated CSI to the base station and demodulating data based on the channel estimated using the CRS.
  • CRS cell-specific reference signal
  • CSI-RS channel state information-reference signal
  • a user equipment device estimating a channel in a wireless communication system includes a transmission module, a reception module and a processor, the processor configured to receive a cell-specific reference signal (CRS) and a channel state information-reference signal (CSI-RS) from a base station using the reception module, the processor configured to generate CSI on a channel estimated using the CSI-RS and CSI on a channel estimated using the CRS based on a mapping relation between a CRS port and a CSI-RS port, the processor configured to report the generated CSI to the base station using the transmission module, the processor configured to demodulate data based on the channel estimated using the CRS.
  • CRS cell-specific reference signal
  • CSI-RS channel state information-reference signal
  • mapping relation between the CRS port and the CSI-RS port is defined as
  • CSIRS p corresponds to a number of the CSI-RS port
  • y i corresponds to an i th CSI-RS port
  • CRS p corresponds to a number of the CRS port
  • Z j corresponds to a j th CRS port
  • M may correspond to a matrix indicating the mapping relation between the CRS port and the CSI-RS port.
  • the matrix M may correspond to a composition matrix consisting of an identity matrix or identity rows.
  • a mapping relation between a layer of the data and the CRS port is defined as
  • [ z 0 ⁇ z CRSp - 1 ] W ⁇ [ x 1 ⁇ x l ]
  • CRS p corresponds to a number of the CRS port
  • Z j corresponds to a j th CRS port
  • 1 corresponds to a number of the layer of the data
  • X k corresponds to a k th layer
  • W may correspond to a precoding matrix applied to the data.
  • the W corresponds to 1 and if two or more CSI-RS port are configured, the W may correspond to the precoding matrix applied to the data.
  • a mapping relation between a layer of the data and the CSI-RS port is defined as
  • CSIRS p corresponds to a number of the CSI-RS port
  • y i corresponds to an i th CSI-RS port
  • 1 corresponds to a number of the layer of the data
  • X k corresponds to a k th layer
  • M corresponds to the mapping relation between the CRS port and the CSI-RS port
  • W may correspond to a precoding matrix applied to the data.
  • a mapping relation between a layer of the data, the CRS port and the CSI-RS port is defined as
  • CSIRS p corresponds to a number of the CSI-RS port
  • y i corresponds to an i th CSI-RS port
  • CRS p corresponds to a number of the CRS port
  • Z j corresponds to a j th CRS port
  • 1 corresponds to a number of the layer of the data
  • X k corresponds to a k th layer
  • M corresponds to the mapping relation between the CRS port and the CSI-RS port
  • W may correspond to a precoding matrix applied to the data.
  • a maximum rank fed back by the user equipment maybe configured by a minimum value among a number of the CSI-RS port and a number of the CRS port.
  • a number of the CSI-RS port may be configured identical to a number of the CRS port.
  • the CSI may be calculated based on an assumption that no UE-specific reference signal exists.
  • the data is demodulated based on the CRS in a subframe configured as a non-MBSFN (multicast-broadcast single frequency network) subframe and the data may be demodulated based on a UE-specific reference signal in a subframe configured as an MBSFN subframe.
  • MBSFN multicast-broadcast single frequency network
  • the data may be demodulated based on the CRS in a non-MBSFN subframe and an MBSFN subframe.
  • the generating the CSI may include the steps of generating a first CSI based on the channel estimated using the CSI-RS and generating a second CSI by modifying the first CSI based on the mapping relation between the CRS port and the CSI-RS port. And, the reporting the CSI may include transmitting the second CSI.
  • the user equipment may be configured with a transmission mode for calculating the first CSI using the CSI-RS and performing demodulation using the CRS.
  • a method of precisely and efficiently determining channel state information on a channel used for performing data demodulation may be provided.
  • a method for a user equipment to compensate for a difference between a channel based on the CRS and a channel based on the CSI-RS may be provided.
  • a method for a base station to compensate for the difference between the channel based on the CRS and the channel based on the CSI-RS ca be provided.
  • FIG. 1 is a diagram for explaining a structure of a radio frame
  • FIG. 2 is a diagram for a resource grid
  • FIG. 3 is a diagram for a structure of a downlink subframe
  • FIG. 4 is a diagram for a structure of an uplink subframe
  • FIG. 5 is diagram for explaining a downlink reference signal
  • FIG. 6 is a diagram for an example of a DMRS pattern defined in LTE-A system
  • FIG. 7 is a diagram for examples of a CSI-RS pattern defined in LTE-A system.
  • FIG. 8 is a diagram for explaining a relationship between a data, a DMRS, a CSI-RS and a CRS port in a TM 9;
  • FIG. 9 is a diagram for explaining a relationship between a data, a CSI-RS and a CRS port in a TM X;
  • FIG. 10 is a diagram for explaining a relationship between a data, a CSI-RS and a CRS port according to one example of the present invention.
  • FIG. 11 is a flowchart for a channel estimating method using a reference signal according to the present invention.
  • FIG. 12 is a diagram for a configuration of a preferred embodiment for a user equipment device according to the present invention.
  • the following embodiments may correspond to combinations of elements and features of the present invention in prescribed forms. And, it may be able to consider that the respective elements or features may be selective unless they are explicitly mentioned. Each of the elements or features may be implemented in a form failing to be combined with other elements or features. Moreover, it may be able to implement an embodiment of the present invention by combining elements and/or features together in part. A sequence of operations explained for each embodiment of the present invention may be modified. Some configurations or features of one embodiment may be included in another embodiment or may be substituted for corresponding configurations or features of another embodiment.
  • a base station has a meaning of a terminal node of a network directly communicating with a user equipment.
  • a specific operation explained as performed by a base station may be performed by an upper node of the base station in some cases.
  • Base station may be substituted with such a terminology as a fixed station, a Node B, an eNode B (eNB), an access point (AP) and the like.
  • a relay may be substituted with such a terminology as a relay node (RN), a relay station (RS), and the like.
  • terminal may be substituted with such a terminology as a user equipment (UE), an MS (mobile station), an MSS (mobile subscriber station), an SS (subscriber station), or the like.
  • Embodiments of the present invention may be supported by the standard documents disclosed in at least one of wireless access systems including IEEE 802 system, 3GPP system, 3GPP LTE system, 3GPP LTE-A (LTE-Advanced) system and 3GPP2 system.
  • wireless access systems including IEEE 802 system, 3GPP system, 3GPP LTE system, 3GPP LTE-A (LTE-Advanced) system and 3GPP2 system.
  • the steps or parts, which are not explained to clearly reveal the technical idea of the present invention in the embodiments of the present invention may be supported by the above documents.
  • all terminologies disclosed in this document may be supported by the above standard documents.
  • CDMA code division multiple access
  • FDMA frequency division multiple access
  • TDMA time division multiple access
  • OFDMA orthogonal frequency division multiple access
  • SC-FDMA single carrier frequency division multiple access
  • CDMA may be implemented with such a radio technology as UTRA (universal terrestrial radio access), CDMA 2000 and the like.
  • TDMA may be implemented with such a radio technology as GSM/GPRS/EDGE (Global System for Mobile communications)/General Packet Radio Service/Enhanced Data Rates for GSM Evolution).
  • OFDMA may be implemented with such a radio technology as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (Evolved UTRA), etc.
  • UTRA is a part of UMTS (Universal Mobile Telecommunications System).
  • 3GPP (3 rd Generation Partnership Project) LTE (long term evolution) is a part of E-UMTS (Evolved UMTS) that uses E-UTRA.
  • the 3GPP LTE adopts OFDMA in downlink (hereinafter abbreviated DL) and SC-FDMA in uplink (hereinafter abbreviated UL).
  • LTE-A LTE-Advanced
  • LTE-A LTE-Advanced
  • WiMAX may be explained by IEEE 802.16e standard (e.g., WirelessMAN-OFDMA reference system) and advanced IEEE 802.16m standard (e.g., WirelessMAN-OFDMA advanced system).
  • IEEE 802.16e standard e.g., WirelessMAN-OFDMA reference system
  • advanced IEEE 802.16m standard e.g., WirelessMAN-OFDMA advanced system.
  • 3GPP LTE and LTE-A standards by which the technical idea of the present invention may be non-limited.
  • a structure for a radio frame of 3GPP LTE system is explained with reference to FIG. 1 .
  • UL/DL (uplink/downlink) data packet transmission is performed by a unit of subframe. And, one subframe is defined as a predetermined time interval including a plurality of OFDM symbols.
  • a type 1 radio frame structure applicable to FDD (frequency division duplex) and a type 2 radio frame structure applicable to TDD (time division duplex) are supported.
  • FIG. 1 ( a ) is a diagram for a structure of a type 1 radio frame.
  • a DL (downlink) radio frame includes 10 subframes. Each of the subframes includes 2 slots in time domain. And, a time taken to transmit one subframe is defined as a transmission time interval (hereinafter abbreviated TTI). For instance, one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms.
  • One slot may include a plurality of OFDM symbols in time domain and may include a plurality of resource blocks (RBs) in frequency domain. Since 3GPP LTE system uses OFDMA in downlink, OFDM symbol is provided to indicate one symbol interval. The OFDM symbol may be named SC-FDMA symbol or symbol interval.
  • Resource block (RB) is a resource allocation unit and may include a plurality of contiguous subcarriers in one slot.
  • the number of OFDM symbols included in one slot may vary in accordance with a configuration of CP (cyclic prefix).
  • the CP may be categorized into an extended CP and a normal CP. For instance, in case that OFDM symbols are configured by the normal CP, the number of OFDM symbols included in one slot may correspond to 7. In case that OFDM symbols are configured by the extended CP, since a length of one OFDM symbol increases, the number of OFDM symbols included in one slot may be smaller than that of the case of the normal CP. In case of the extended CP, for instance, the number of OFDM symbols included in one slot may correspond to 6. If a channel status is unstable (e.g., a UE is moving at high speed), it may be able to use the extended CP to further reduce the inter-symbol interference.
  • FIG. 1 ( b ) is a diagram for a structure of a downlink radio frame of type 2.
  • a type 2 radio frame includes 2 half frames. Each of the half frame includes 5 subframes, a DwPTS (downlink pilot time slot), a GP (guard period), and an UpPTS (uplink pilot time slot). Each of the subframes includes 2 slots.
  • the DwPTS is used for initial cell search, synchronization, or a channel estimation in a user equipment.
  • the UpPTS is used for channel estimation of a base station and matching a transmission synchronization of a user equipment.
  • the guard period is a period for eliminating interference generated in uplink due to multi-path delay of a downlink signal between uplink and downlink. Meanwhile, one subframe includes 2 slots irrespective of a type of a radio frame.
  • the above-described structures of the radio frame are exemplary only. And, the number of subframes included in a radio frame, the number of slots included in the subframe and the number of symbols included in the slot may be modified in various ways.
  • FIG. 2 is a diagram for a resource grid in a downlink slot.
  • one downlink (DL) slot includes 7 OFDM symbols in time domain and one resource block (RB) includes 12 subcarriers in frequency domain, by which the present invention may be non-limited.
  • one slot includes 7 OFDM symbols.
  • one slot may include 6 OFDM symbols.
  • Each element on a resource grid is called a resource element.
  • One resource block includes 12 ⁇ 7 resource elements.
  • the number N DL of resource blocks included in a DL slot may depend on a DL transmission bandwidth.
  • the structure of an uplink (UL) slot may be identical to that of the DL slot.
  • FIG. 3 is a diagram for a structure of a downlink (DL) subframe.
  • Maximum 3 OFDM symbols situated in a head part of a first slot of one subframe correspond to a control region to which control channels are assigned.
  • the rest of OFDM symbols correspond to a data region to which PDSCH (physical downlink shared channel) is assigned.
  • Examples of DL control channels used by 3GPP LTE system may include PCFICH (Physical Control Format Indicator Channel), PDCCH (Physical Downlink Control Channel), PHICH (Physical hybrid automatic repeat request indicator Channel) and the like.
  • the PCFICH is transmitted in a first OFDM symbol of a subframe and includes information on the number of OFDM symbols used for a transmission of a control channel within the subframe.
  • the PHICH is a response channel in response to UL transmission and includes an ACK/NACK signal.
  • Control information carried on PDCCH may be called downlink control information (hereinafter abbreviated DCI).
  • the DCI may include UL scheduling information, DL scheduling information or a UL transmit power control command for a random UE (user equipment) group.
  • PDCCH is able to carry resource allocation and transmission format (or called a DL grant) of DL-SCH (downlink shared channel), resource allocation information (or called a UL grant) of UL-SCH (uplink shared channel), paging information on PCH (paging channel), system information on DL-SCH, resource allocation to an upper layer control message such as a random access response transmitted on PDSCH, a set of transmission power control commands for individual user equipments within a random user equipment (UE) group, activation of VoIP (voice over IP) and the like.
  • a plurality of PDCCHs may be transmitted in a control region and a user equipment is able to monitor a plurality of the PDCCHs.
  • PDCCH is configured with the aggregation of at least one or more contiguous CCEs (control channel elements).
  • CCE is a logical assignment unit used to provide PDCCH with a code rate in accordance with a state of a radio channel.
  • CCE corresponds to a plurality of REGs (resource element groups).
  • a format of PDCCH and the number of bits of an available PDCCH are determined depending on correlation between the number of CCEs and a code rate provided by the CCEs.
  • a base station determines PDCCH format in accordance with DCI to transmit to a user equipment and attaches CRC (cyclic redundancy check) to control information.
  • CRC cyclic redundancy check
  • the CRC is masked with a unique identifier (called RNTI (radio network temporary identifier) in accordance with an owner or usage of PDCCH.
  • RNTI radio network temporary identifier
  • the CRC may be masked with a unique identifier of the user equipment, i.e., C-RNTI (i.e., Cell-RNTI).
  • C-RNTI i.e., Cell-RNTI
  • the CRC may be masked with a paging indication identifier (e.g., P-RNTI (Paging-RNTI)).
  • the CRC may be masked with a system information identifier (e.g., SI-RNTI (system information-RNTI).
  • SI-RNTI system information-RNTI
  • RA-RNTI random access-RNTI
  • FIG. 4 is a diagram for a structure of an uplink (UL) subframe.
  • a UL subframe may be divided into a control region and a data region in frequency domain.
  • a physical UL control channel (PUCCH) which includes UL control information, is assigned to the control region.
  • a physical UL shared channel (PUSCH) which includes user data, is assigned to the data region.
  • PUCCH for one user equipment is assigned to a resource block pair (RB pair) in a subframe. Resource blocks belonging to the resource block (RB) pair may occupy different subcarriers in each of 2 slots. Namely, a resource block pair allocated to PUCCH is frequency-hopped on a slot boundary.
  • a signal When a packet is transmitted in a wireless communication system, since the packet is transmitted via a radio channel, a signal may be distorted in the course of transmission. In order for a receiving end to correctly receive a distorted signal, it may be preferable that the distorted and received signal is corrected using channel information. In order to find out the channel information, a signal known to both of a transmitting end and the receiving end is transmitted and finds out the channel information with the extent of distortion when the signal is received on a channel. The signal is called a pilot signal or a reference signal.
  • each transmitting antenna of the transmitting end may preferably have an individual reference signal.
  • DL reference signals are classified into a common reference signal (CRS) shared by all user equipments in one cell and a dedicated reference signal (DRS) for a specific user equipment only.
  • the transmitting end may be able to provide the receiving end with information for demodulation and channel measurement using these reference signals (i.e., CRS and DRS).
  • the receiving end measures a channel state using the CRS and may be then able to feed back such an indicator related to a channel equality as a channel quality indicator (CQI), a precoding matrix index (PMI), a rank indicator (RI) and the like to the transmitting end (e.g. a base station) in response to the measured channel state.
  • CRS may be named a cell-specific reference signal (cell-specific RS).
  • CSI-RS channel state information
  • DRS may be transmitted to user equipments via resource elements if data demodulation on PDSCH is required.
  • a user equipment may be able to receive a presence or non-presence of DRS through upper layer signaling.
  • the DRS is effective only if mapped by a corresponding PDSCH signal.
  • DRS may be called a user equipment-specific reference signal (UE-specific RS) or a demodulation reference signal (DMRS).
  • UE-specific RS user equipment-specific reference signal
  • DMRS demodulation reference signal
  • FIG. 5 is a diagram for a pattern of CRS and DRS defined by a legacy 3GPP LTE system (e.g., release-8) mapped to a downlink resource block (RB) pair.
  • the downlink resource block pair as a unit of mapping a reference signal may be represented as ‘one subframe in time domain*12 subcarriers in frequency domain’.
  • one resource block pair on a time axis (x axis) has a length of 14 OFDM symbols in case of a normal cyclic prefix (normal CP) and has a length of 12 OFDM symbols in case of an extended cyclic prefix (extended CP).
  • FIG. 5 shows a resource block pair in case of a normal CP.
  • FIG. 5 shows positions of reference signals on a resource block pair in a system supporting 4 antennas by a base station.
  • resource elements (RE) represented as ‘R0’, ‘R1’, ‘R2’, and ‘R3’ indicate positions of the CRS for an antenna port 0, 1, 2, and 3, respectively.
  • resource elements represented as ‘ID’ in FIG. 5 indicates positions of the DRS.
  • the CRS is used to estimate a channel of a physical antenna and is distributed to a whole frequency band as a reference signal capable of being commonly received by all user equipments situated within a cell. And, the CRS may be used for channel quality information (CSI) and a data demodulation.
  • CSI channel quality information
  • the CRS is defined by various formats according to antenna configuration of a transmitting side (base station).
  • 3GPP LTE system e.g., release-8) supports various antenna configurations.
  • a DL signal transmitting side e.g., base station
  • includes 3 kinds of antenna configuration such as a single transmitting antenna, 2 transmitting antennas, and 4 transmitting antennas.
  • a base station uses a single transmitting antenna
  • a reference signal for a single antenna port is arranged.
  • the reference signal for 2 transmitting antennas ports is arranged using a time division multiplexing (TDM) scheme and/or a frequency division multiplexing (FDM) scheme.
  • TDM time division multiplexing
  • FDM frequency division multiplexing
  • the reference signal for the 2 antennas ports is arranged using the TDM scheme and/or the FDM scheme.
  • Channel information estimated by a DL signal receiving side may be used to demodulate the data transmitted using such a transmission scheme as a single antenna transmission, a transmission diversity, a closed-loop spatial multiplexing, an open-loop spatial multiplexing, or a multi-user MIMO.
  • a MIMO antenna when a reference signal is transmitted from a specific antenna port, the reference signal is transmitted to the position of resource elements specified according to a reference signal pattern and is not transmitted to the position of resource elements specified for a different antenna port.
  • a rule of mapping CRC to a resource block is defined as follows.
  • k and l indicate a subcarrier index and a symbol index, respectively.
  • P indicates an antenna port index.
  • N symb DL indicates the number of OFDM symbol in one DL slot and N RB EL indicates the number of radio resource allocated to a downlink.
  • n s indicates a slot index and N ID cell indicates a cell ID.
  • a mod indicates a modulo calculation.
  • a position of the reference signal in frequency domain varies depends on a V shift value. Since the V shift value depends on the cell ID, the position of the reference signal may have different frequency shift values according to a cell.
  • the position of the CRS may be shifted in frequency domain according to a cell. For instance, in case that a reference signal is positioned with an interval of 3 subcarriers, reference signals in one cell are assigned to a n th subcarrier and the reference signal in a different cell is assigned to a (3k+1) th subcarrier. In a single antenna port point of view, reference signals are arranged with an interval of 6 resource elements in frequency domain and separated from the reference signal assigned to a different antenna port with an interval of 3 resource elements.
  • power boosting may be applied to a CRS.
  • the power boosting means to transmit a reference signal with higher power in a manner of bring power from a different RE instead of the RE allocated for the reference signal among the REs in one OFDM symbol.
  • a position of a reference signal in time domain is arranged starting from a symbol index (1) 0 of each slot with a constant interval.
  • Time interval is differently defined according to a length of a cyclic prefix.
  • the reference signal In case of a normal cyclic prefix, the reference signal is positioned at the symbol index 0 and 4 of a slot. In case of an extended prefix, the reference signal is positioned at the symbol index 0 and 3 of a slot.
  • the reference signal which is required for the antenna port having a maximum value among the 2 antenna ports, is defined within an OFDM symbol.
  • the reference signal for the antenna port 0 and 1 is positioned at the symbol index 0 and 4 of a slot (in case of extended prefix, symbol index 0 and 3) and the reference signal for the antenna port 2 and 3 is positioned at the symbol index 1 of a slot.
  • the position of the reference signal for the antenna port 2 and 3 in frequency domain is exchanged with each other in a 2 nd slot.
  • the DRS (or UE-specific reference signal) is used to demodulate data.
  • a precoding weighted value used for a specific user equipment is used for a reference signal as it is. By doing so, when a user equipment receives the reference signal, the user equipment may estimate an equivalent channel corresponding to a channel with which a precoding weighted value transmitted from each transmitting antenna and a transport channel are combined.
  • a legacy 3GPP LTE system (e.g., release-8) supports maximum 4 transmitting antennas and defines a DRS for a rank 1 beamforming.
  • the DRS for the rank 1 beamforming may indicate a reference signal for an antenna port index 5 as well.
  • a rule of mapping DRS to a resource block is defined as follows. Formula 2 indicates a case of a normal cyclic prefix.
  • k and l indicate a subcarrier index and a symbol index, respectively.
  • P indicates an antenna port index.
  • N SC RB indicates a size of a resource block in frequency domain and is represented as the number of subcarrier.
  • n PRB indicates the number of physical resource block.
  • N RB PDSCH indicates a frequency band of a resource block for a PDSCH transmission.
  • n s indicates a slot index and N ID cell indicates a cell ID.
  • mod indicates a modulo calculation.
  • a position of the reference signal depends on a V shift value in frequency domain. Since the V shift value depends on the cell ID, the position of the reference signal may have different frequency shift values according to a cell.
  • LTE-A advanced MU-MIMO
  • LTE-A evolved version of 3GPP LTE.
  • DRS-based data demodulation is considering.
  • a DRS antenna port index 5
  • a DRS UE-specific reference signal or DMRS
  • DMRS UE-specific reference signal
  • FIG. 6 is a diagram for an example of a DMRS pattern defined in LTE-A system.
  • FIG. 6 shows a position of a resource element to which a DMRS is transmitted on one resource block pair (in case of a normal CP, 14 OFDM symbols in time domain ⁇ 12 subcarriers in frequency domain) in which DL data is transmitted.
  • the DMRS may be transmitted in response to 8 antenna ports (antenna port index 7 to 14) additionally defined in LTE-A system.
  • the DMRS for antenna ports different from each other may be distinguished from each other in a manner of being positioned at frequency resources (subcarriers) different from each other and/or time resources (OFDM symbols) different from each other (i.e., the DM RS for antenna ports different from each other may be multiplexed by FDM and/or TDM scheme).
  • the DMRS for antenna ports different from each other positioned at an identical time-frequency resource may be distinguished from each other by an orthogonal code (i.e., the DMRS for antenna ports different from each other may be multiplexed by CDM scheme).
  • CSI-RS which is used for measuring channel state information for a new antenna port
  • an advanced wireless communication system e.g., LTE-A system
  • FIG. 7 is a diagram for examples of a CSI-RS pattern defined in LTE-A system.
  • FIG. 7 shows a position of a resource element to which a CSI-RS is transmitted on one resource block pair (in case of a normal CP, 14 OFDM symbols in time domain ⁇ 12 subcarriers in frequency domain) in which DL data is transmitted.
  • One CSI-RS pattern among patterns depicted in FIG. 7 ( a ) to FIG. 7 ( e ) may be used in a prescribed DL subframe.
  • the CSI-RS may be transmitted in response to 8 antenna ports (antenna port index 15, 16, 17, 18, 19, 20, 21 and 22) additionally defined in LTE-A system.
  • the CSI-RS for antenna ports different from each other may be distinguished from each other in a manner of being positioned at frequency resources (subcarriers) different from each other and/or time resources (OFDM symbols) different from each other (i.e., the CSI-RS for antenna ports different from each other may be multiplexed by FDM and/or TDM scheme). And, the CSI-RS for antenna ports different from each other positioned at an identical time-frequency resource may be distinguished from each other by an orthogonal code (i.e., the CSI-RS for antenna ports different from each other may be multiplexed by CDM scheme). Referring to the example of FIG.
  • CSI-RSs for an antenna port 15 and 16 may be positioned at resource elements (REs) represented as a CSI-RS CDM group 1 and the CSI-RSs for the antenna port 15 and 16 may be multiplexed by the orthogonal code.
  • CSI-RSs for an antenna port 17 and 18 may be positioned at resource elements (REs) represented as a CSI-RS CDM group 2 and the CSI-RSs for the antenna port 17 and 18 may be multiplexed by the orthogonal code.
  • REs resource elements
  • FIG. 7 ( a ) CSI-RSs for an antenna port 17 and 18 may be positioned at resource elements (REs) represented as a CSI-RS CDM group 2 and the CSI-RSs for the antenna port 17 and 18 may be multiplexed by the orthogonal code.
  • CSI-RSs for an antenna port 19 and 20 may be positioned at resource elements (REs) represented as a CSI-RS CDM group 3 and the CSI-RSs for the antenna port 19 and 20 may be multiplexed by the orthogonal code.
  • CSI-RSs for an antenna port 21 and 22 may be positioned at resource elements (REs) represented as a CSI-RS CDM group 4 and the CSI-RSs for the antenna port 21 and 22 may be multiplexed by the orthogonal code.
  • a principle explained on the basis of FIG. 7 ( a ) may be identically applied to FIG. 7 ( b ) to FIG. 7 ( e ) .
  • the RS patterns depicted in FIG. 5 to FIG. 7 are just examples. Various examples of the present invention may be non-limited to a specific RS pattern. In particular, in case of using an RS pattern different from the RS patterns depicted in FIG. 5 to FIG. 7 , various embodiments of the present invention may also be identically applied to the RS pattern.
  • CoMP Cooperative Multi-Point
  • a CoMP transmission/reception technology MIMO (represented as a co-MIMO, a collaborative MIMO, a network MIMO, or the like) is proposed.
  • the CoMP technology increases the performance of a user equipment situating at a cell edge and may increase an average sector throughput.
  • ICI inter-cell interference
  • a legacy LTE system has applied a method for enabling the user equipment situating at a cell boundary to have an appropriate throughput performance using such a simple passive scheme as a fractional frequency reuse (FFR) via a UE-specific power control in an environment limited by the interference.
  • FFR fractional frequency reuse
  • CoMP transmission scheme may be applied.
  • the CoMP scheme applicable in DL may be largely classified into a joint processing (JP) scheme and a coordinated scheduling/beamforming (CS/CB) scheme.
  • JP joint processing
  • CS/CB coordinated scheduling/beamforming
  • the JP scheme may use a data in each point (base station) of a CoMP cooperative unit.
  • the CoMP cooperative unit means a set of base stations used for a cooperative transmission scheme.
  • the JP scheme may be classified into a joint transmission scheme and a dynamic cell selection scheme.
  • the joint transmission scheme indicates a scheme transmitting PDSCH from a plurality of points (a part or entire CoMP cooperative units) at a time.
  • the data transmitted to single user equipment may be simultaneously transmitted from a plurality of transmission points.
  • quality of a reception signal may be coherently or non-coherently enhanced. And, interference for a different user equipment may be actively eliminated.
  • the dynamic cell selection scheme indicates a scheme transmitting PDSCH from a point (of a CoMP cooperative unit) at a time.
  • a data transmitted to single user equipment on a specific timing point is transmitted from one point.
  • a different point within the cooperative unit does not transmit a data to the corresponding user equipment on the specific timing point.
  • the point transmitting the data to the corresponding user equipment may be dynamically selected.
  • the CoMP cooperative units may cooperatively perform a beamforming of data transmission for single user equipment.
  • a user scheduling/beamforming may be determined by a coordination of cells in a corresponding CoMP cooperative unit.
  • a coordinated multi-point reception means to receive a signal transmitted by coordination of a plurality of points, which are geographically apart from each other.
  • the CoMP scheme applicable to a case of UL may be classified into a joint reception (JR) and the coordinated scheduling/beamforming (CS/CB).
  • the JR scheme means that a signal transmitted on PUSCH is received by a plurality of receiving points.
  • the CS/CB scheme means that PUSCH is received at one point and a user scheduling/beamforming is determined by coordination of cells in a CoMP cooperative unit.
  • multi-cell base station may commonly support data for a user equipment. And, each of the base stations supports one or more user equipments at the same time using a same radio frequency resource, thereby improving system performance. Moreover, a base station may perform a space division multiple access (SDMA) based on channel state information between the base station and a user equipment.
  • SDMA space division multiple access
  • a serving base station and one or more cooperative base stations are connected with a scheduler via a backbone network.
  • the scheduler may operate in a manner of receiving feedback of channel information on channel state between each user equipment and a cooperative base station measured by each base station via the backbone network. For instance, the scheduler may schedule information for a cooperative MIMO operation for the serving base station and the one or more cooperative base stations. In particular, the scheduler may directly give direction on the cooperative MIMO operation to each base station.
  • the CoMP system may correspond to a system operating as a virtual MIMO system in a manner of binding a plurality of cells into one group.
  • a communication scheme of a MIMO system using a plurality of antennas may be applied to the CoMP system.
  • a new transmission mode differentiated from a legacy transmission mode is defined in a system (e.g., LTE-A system) to which a CSI-RS is introduced.
  • a UE generates CSI feedback information (e.g., RI, PMI and/or CQI) based on a channel measured/estimated based on a CSI-RS and may perform demodulation based on a channel measured/estimated based on a DMRS (or UE-specific RS or DRS).
  • CSI feedback information e.g., RI, PMI and/or CQI
  • the UE may properly demodulate the data based on a channel (i.e., precoded channel) estimated from the DMRS although the base station does not separately inform the UE of precoding information which is applied to the DMRS.
  • a channel i.e., precoded channel
  • the base station may use non-codebook based precoding in a manner of freely determining a transmission beam. By doing so, the base station may secure sufficient spatial freedom for implementing MU-MIMO or CoMP.
  • the aforementioned new transmission mode is called a transmission mode X (TM X).
  • TM X transmission mode X
  • the present invention examines a problem which may occur when the CSI feedback information is generated based on channel estimation using the CSI-RS in accordance with the TM X and demodulation is performed based on channel estimation using the CRS and proposes a method capable of solving the problem.
  • FIG. 8 is a diagram for explaining a relationship between a data, a DMRS, a CSI-RS and a CRS port in a TM 9. Specifically, FIG. 8 shows mapping relations between logical antenna ports of DMRS, CSI-RS and CRS and a physical antenna port in the TM 9. And, FIG. 8 also shows a mapping relation between data (e.g., PDSCH corresponding to a user data transmission channel) and the logical antenna port.
  • data e.g., PDSCH corresponding to a user data transmission channel
  • a data transmission layer e.g., PDSCH transmission layer
  • a DMRS port e.g., antenna port number 7 to 14
  • the PDSCH transmission layer 0 to 7 may be mapped to DMRS port 7 to 14, respectively.
  • FIG. 8 shows a relation that data (e.g., PDSCH transmission layer) is mapped to a DMRS port via an identity matrix.
  • the DMRS port is mapped to a CSI-RS port via precoding. For instance, in case of performing a CSI report in the TM 9, a PDSCH signal on the DMRS port 7 to 14 for 8 layers corresponds to a symbol transmitted on the CSI-RS port 15 to 22. A relation between a PDSCH transmission layer and the CSI-RS port may be determined by a precoding matrix. In particular, the DMRS port 7 to 14 is mapped to the CSI-RS port 15 to 22 by the precoding matrix.
  • FIG. 8 shows an antenna virtualization matrix 1 and an antenna virtualization matrix 2.
  • the antenna virtualization matrix is a matrix defining a mapping relation between the logical antenna port and the physical antenna port.
  • the CSI-RS port is mapped to the physical antenna port via the antenna virtualization matrix 1 configured by a base station.
  • the DMRS port is mapped to the physical antenna port via the antenna virtualization matrix 1.
  • the logical antenna port (i.e., CSI-RS port 15 to 22) used for channel estimation on the timing of generating CSI and the logical antenna port (i.e., DMRS port 7 to 14) used for channel estimation on the timing of demodulating the CSI are different from each other in terms of a logical antenna port number, if precoding is not considered (e.g., if a precoding matrix corresponds to 1 or I), an identical channel is estimated when the CSI is generated and demodulated.
  • the CRS port (antenna port 0 to 3) is mapped to the physical antenna port via the antenna virtualization matrix 2 independent of the antenna virtualization matrix 1, which is applied to the DMRS port and the CSI-RS port.
  • the antenna virtualization according to the TM 9 mentioned earlier in FIG. 8 is not applied as it is.
  • FIG. 9 is a diagram for explaining a relationship between a data, a CSI-RS and a CRS port in a TM X. For clarity, FIG. 9 does not show a DMRS since a channel is estimated using CRS for data demodulation.
  • independent antenna virtualization matrixes are applied to a CSI-RS port and a CRS port, respectively.
  • an antenna virtualization matrix 1 may be applied to the CSI-RS port (i.e., antenna port 15 to 22) and an antenna virtualization matrix 2 may be applied to the CRS port (i.e., antenna port 0 to 3).
  • data e.g., PDSCH transmission layer
  • the antenna virtualization matrix 2 may be applied to the data.
  • the antenna virtualization matrix 1 and 2 are represented as V1 and V2, respectively and an actual channel is represented as a matrix H.
  • a UE may generate and feedback CSI information on an effective channel (H*V1) using the CSI-RS.
  • the effective channel carrying data corresponds to not (H*V1) but (H*V2), there may occur a problem that the CSI information calculated based on the (H*V1) may not properly indicates a state of the (H*V2) corresponding to a channel carrying the data.
  • the present invention proposes a method of compensating for a difference between the channel estimated using the CSI-RS and the channel estimated using the CRS.
  • a base station maps the CRS port onto the CSI-RS port and may inform a UE of information indicating a mapping relation.
  • the UE may generate, calculate and report CSI in a manner of assuming the mapping relation and reflecting a difference between a channel estimated from a CSI-RS and a channel on which an actual data is transmitted.
  • FIG. 10 is a diagram for explaining a relationship between a data, a CSI-RS and a CRS port according to one example of the present invention.
  • a relation between antenna ports may be represented as FIG. 10 .
  • the CRS port is mapped to the CSI-RS port via the matrix M and the CRS port and the CSI-RS port may be commonly mapped to the physical antenna port via an antenna virtualization matrix 1 (i.e., V1).
  • V1 antenna virtualization matrix 1
  • a UE generates CSI on an effective channel H*V1 using a CSI-RS and may generate a final CSI feedback information in consideration of the matrix M indicating a mapping relation between the CRS port and the CSI-RS port.
  • the UE may compensate for a difference between a channel estimated using the CSI-RS and a channel estimated using the CRS.
  • y i indicates i th CSI-RS port (or CSI-RS port number i) and z j indicates j th CRS port (or CRS port number j).
  • the Formula 3 indicates a mapping relation between 2 CRC ports (i.e., CRS port 0 and 1) and 2 CSI-RS ports (i.e., CSI-RS port 15 and 16).
  • the Formula 4 indicates a mapping relation between 4 CRC ports (i.e., CRS port 0 to 3) and 4 CSI-RS ports (i.e., CSI-RS port 15 to 18).
  • the Formula 5 indicates a mapping relation between 4 CRC ports (i.e., CRS port 0 to 3) and 2 CSI-RS ports (i.e., CSI-RS port 15 and 16).
  • the Formula 6 indicates a mapping relation between 2 CRC ports (i.e., CRS port 0 and 1) and 4 CSI-RS ports (i.e., CSI-RS port 15 to 18).
  • the Formula 7 indicates a mapping relation between 2 CRC ports (i.e., CRS port 0 and 1) and 8 CSI-RS ports (i.e., CSI-RS port 15 to 22).
  • the Formula 8 indicates a mapping relation between 4 CRC ports (i.e., CRS port 0 to 3) and 8 CSI-RS ports (i.e., CSI-RS port 15 to 22).
  • M corresponds to a matrix indicating a mapping between ports.
  • m ij (an element or a factor corresponding to i th column and j th row in the matrix M) has a value of 1 or 0. If the m ij corresponds to 1, a CRS port j and a CSI-RS port i are mapped to each other. If the m u corresponds to 0, mapping is not performed.
  • a CRS port 0 is mapped to a CSI-RS port 15 and a CRS port 1 is mapped to a CSI-RS port 16.
  • the CRS port 0, 1, 2 and 3 are mapped to the CSI-RS port 15, 16, 16 and 18, respectively.
  • the M may have a form that identity matrixes are combined with each other.
  • the M may correspond to [I I], [I I] T , [I I I] T and [I I] T , respectively.
  • a T indicates a transposed matrix of a matrix A.
  • a mapping relation between the CRS port and the CSI-RS port may also be represented as the M.
  • a matrix M may be configured with a fixed value. Or, the matrix M may be semi-statically configured. Information on the matrix M may be provided to a UE via an upper layer (e.g., RRC (radio resource control) layer) signaling.
  • RRC radio resource control
  • a Formula 9 in the following corresponds to an expression that generalizes the examples of the Formula 3 to 8.
  • CRS p indicates the number of CRS port and CSIRS p indicates the number of CSI-RS port.
  • M may correspond to composition matrix consisting of an identity matrix or identity rows.
  • mapping relation between the CRS port and x may be represented as Formula 10 in the following.
  • CRS p indicates the number of CRS port and 1 indicates the number of layer.
  • x k indicates a k th layer.
  • W corresponds to 1. Otherwise (i.e., if two or more CSI-RS ports are configured), W may corresponds to a precoding matrix corresponding to PMI, which is applicable to x.
  • a mapping relation between a multiple layer data stream x and a CSI-RS port may be represented as Formula 11 in the following.
  • CSIRS p indicates the number of CSI-RS port and 1 indicates the number of layer. And, in case that one CSI-RS port is configured only, W corresponds to 1. Otherwise (i.e., if two or more CSI-RS ports are configured), W may corresponds to a precoding matrix corresponding to PMI, which is applicable to x. and, M may correspond to a matrix indicating a mapping relation between a CRS port and a CSI-RS port.
  • Formula 9 and 10 When the Formula 9 and 10 are considered at the same time, it may be represented as Formula 12 in the following.
  • CSIRS p indicates the number of CSI-RS port and 1 indicates the number of layer. And, in case that one CSI-RS port is configured only, W corresponds to 1. Otherwise (i.e., if two or more CSI-RS ports are configured), W may corresponds to a precoding matrix corresponding to PMI, which is applicable to x. and, M may correspond to a matrix indicating a mapping relation between a CRS port and a CSI-RS port.
  • a restriction described in the following may be defined. For instance, it may consider a rank restriction and/or a port restriction.
  • a maximum rank capable of being fed back by a UE may be configured by a minimum value among the number of CSI-RS port and the number of CRS port.
  • the number of CSI-RS port is greater than the number of CRS port, since the maximum rank of a channel, which is estimated on timing of demodulation, is restricted to be less than the number of CRS port, rank information to be fed back is also restricted to be less than the number of CRS port.
  • the number of CSI-RS port is greater than the number of CRS port, since the maximum rank of a channel, which is measured for CSI feedback, is restricted to the number of CSI-RS port, a maximum value of the rank information to be fed back is also restricted to the number of CSI-RS port.
  • the CSI may be calculated based on an assumption that a DMRS (or UE-specific RS or DRS) is not transmitted.
  • the UE may calculate the CSI in an assumption (e.g., assumption that PDSCH is transmitted to an RE position to which the DMRS is transmittable) that the DMRS overhead corresponds 0.
  • a final CSI may be calculated by utilizing a mapping relation (e.g., matrix M) between the CSI-RS port and the CRS port.
  • the UE may calculate the CSI in a manner of assuming the mapping relation shown in Formula 9 to 12. For instance, the UE may generate/calculate the CSI on a channel for the CRS port based on a channel estimated using the CSI-RS and the mapping relation between the CRS port and the CSI-RS port. The UE calculates a temporary CSI (or first CSI) for the channel (e.g., H*V1) estimated using the CSI-RS, modifies the temporary CSI by considering an effective channel (e.g., H*M*V1) in which the matrix M is considered, and may calculate the final CSI (or a second CSI).
  • a temporary CSI or first CSI
  • H*M*V1 an effective channel
  • a DCI format of downlink scheduling information on the TM X may vary according to whether a fake MBSFN (multicast-broadcast single frequency network) subframe is configured.
  • the fake MBSFN subframe is recognized as a MBSFN subframe to a UE (e.g., legacy UE) operating according to a 3GPP LTE release 8/9 system.
  • the fake MBSFN subframe is recognized as a subframe capable of being used for a different usage instead of MBSFN to a UE (e.g., advanced UE) operating according to 3GPP LTE-A system.
  • a CRS may not be transmitted to a transmission region (e.g., PDSCH region) and data (e.g., PDSCH) is not transmitted or is transmitted with a low transmit power or a general transmit power in the fake MBSFN subframe.
  • the macro cell may configure an ABS (almost blank subframe) to protect the pico cell.
  • the ABS corresponds to a subframe transmitting a CRS only in a control region and a data region (refer to FIG. 3 ) of a downlink subframe and the subframe not transmitting other control information and data.
  • a downlink channel as a PBCH, a PSS, an SSS and the like and a downlink signal may be transmitted in the ABS.
  • the ABS may be additionally configured as the fake MBSFN.
  • a CRS may not be transmitted in a data region in the subframe configured as the fake MBSFN and data (e.g., PDSCH) is not transmitted or is transmitted with a low transmit power or a general transmit power in the fake MBSFN subframe.
  • data e.g., PDSCH
  • a DMRS may be used to demodulate data.
  • demodulation should be performed using the DMRS in the fake MBSFN ABS in the TM X for generating CSI feedback information using a CSI-RS and performing demodulation using a CRS as well.
  • a DCI format informing DMRS information should be provided to a UE.
  • TM X when the TM X is configured, since a CRS exists in a non-MBSFN subframe, CRS-based demodulation is performed instead of DMRS-based modulation.
  • a DCI format including information on a precoder used by a base station should be provided to the UE.
  • a DCI format detected by the UE should be dependently changed according to whether a MBSFN subframe is configured.
  • the UE may detect a DCI format informing the UE of DMRS information in a subframe configured as the MBSFN subframe and detect a DCI format including the information on the precoder used by the base station in a subframe configured as the non-MBSFN subframe.
  • the UE may detect the DCI format informing the UE of DMRS information in the subframe configured as the MBSFN subframe and detect the DCI format including the information on the precoder used by the base station in the subframe configured as the non-MBSFN subframe. And, the UE calculates CSI in a manner of assuming DMRS overhead in the subframe configured as the MBSFN with a scheme identical to the TM 9 and the UE may calculate the CSI in a manner of assuming (e.g., assuming that PDSCH is transmitted to a RE position to which DMRS is transmittable) that the DMRS overhead corresponds to 0 in the subframe configured as the non-MBSFN.
  • the present invention proposes to apply a narrow band CRS.
  • the narrow band CRS means to transmit a CRS to a part of the band.
  • CRS transmission is permitted to a part of RB in the fake MBSFN subframe.
  • the UE may perform demodulation of the data using a narrow band CRS existing in the specific RB.
  • the UE configured with the TM X detects the DCI format including the information on the precoder used by the base station and may be then able to perform downlink reception.
  • a UE generates CSI based on a channel estimated from a CSI-RS and reports the CSI to a base station and the base station may schedule data transmission in consideration of a difference between a channel for a CRS port and a channel for a CSI-RS port.
  • the UE generates the CSI on an effective channel H*V1 using the CSI-RS and may report the CSI to the base station.
  • the base station determines a precoding matrix practically capable of identically matching an effective channel (e.g., H*V1), which is calculated based on the CSI-RS, with an effective channel (e.g., H*V2), which is calculated based on a CRS, using the CSI fed back by the UE based on the CSI-RS.
  • the base station may perform the data transmission based on the determined precoding matrix.
  • the base station may compensate for a difference between the channel estimated using the CSI-RS and the channel estimated using the CRS. This may be represented as Formula 13 in the following.
  • H*V 1 *P 1 H*V 2 *P 2 [Formula 13]
  • P1 corresponds to a precoding matrix corresponding to PMI reported by the UE and P2 may correspond to a precoding matrix used by the base station for the data transmission.
  • H indicates an actual downlink channel
  • V1 corresponds to an antenna virtualization matrix applied to the CSI-RS
  • V2 may correspond to an antenna virtualization matrix applied to the CRS.
  • the base station may obtain the P2 satisfying the aforementioned Formula 13.
  • the P2 is a precoding matrix corresponding to an element (i.e., codeword) in a codebook consisting of a set of quantized precoding matrixes.
  • Information on the P2 may be provided to the UE on a control channel. Since the P2 corresponds to a quantized value including finite precision, there may not exist the P2, which precisely satisfies an equal mark of the Formula 13, in the codebook. Yet, the base station may determine the P2 as an approximate value satisfying the equal mark of the Formula 13 as much as possible.
  • the Formula 13 may also be represented as Formula 14 in the following.
  • H*V 1 *P 1 H*M*V 1 *P 2 [Formula 14]
  • a transmission mode 4 which uses a CRS to perform CSI feedback and demodulation in a legacy 3GPP LTE system, may be used as it is.
  • TM 4 transmission mode 4
  • an upper layer e.g., RRC
  • the information indicating whether to perform the CSI-RS based-CSI feedback is defined by an indicator of 1 bit-long
  • CSI calculated using a CRS is fed back according to the original TM 4 and if the value of the indicator corresponds to 1, CSI calculated using a CSI-RS may be fed back.
  • the UE may calculate the CSI under an assumption that there is no DMRS overhead.
  • an operation based on 2 codebooks may be supported to a system (e.g. 4 transmission antennas or 2 transmission antennas) including a less number of transmission antennas (Tx antenna).
  • a system e.g. 4 transmission antennas or 2 transmission antennas
  • Tx antenna transmission antennas
  • a PMI codebook for 2Tx and 4Tx antenna system is designed by one codebook including 16 elements (i.e., codewords) per each rank.
  • the PMI codebook for 8Tx antenna system determines a precoding matrix by a combination (or multiplication) of two codebooks including a codebook indicating channel information of a long-term attribute and a codebook indicating channel information of a short-term attribute.
  • the 2 codebooks based operation scheme for the 8Tx antennas is more effective in performing feedback on a precise channel.
  • the 2 codebooks based operation scheme may be applied to the 2Tx and/or 4Tx antennas system.
  • the 2 codebooks based operation scheme for the 2Tx and/or 4Tx antennas system may be supported via the aforementioned antenna port mapping while the codebook already designed for the 8Tx antennas system is used without newly designing 2 codebooks for the 2Tx and/or 4Tx antennas system.
  • a UE generates and reports CSI based on the CSI-RS and PMI may be generated/determined based on 2 codebooks. For instance, the UE may report a first PMI (W1 or i1) of a long-term attribute and a second PMI (W2 or i2) of a short-term attribute to a base station.
  • the W1 and the W2 correspond to 2 codebooks based PMI for a channel which is estimated based on 8 ports CSI-RS.
  • a mapping relation between a CSI-RS port and a CRS port may be given as a matrix M.
  • the UE may change CSI (e.g. first CSI) calculated based on the CSI-RS to CSI (e.g., second CSI) based on the CRS port in consideration of the matrix M.
  • the W1 and the W2 correspond to the first CSI and ‘M*W1’ and ‘M*W2’ may correspond to the second CSI.
  • the UE may directly calculate the second CSI without passing through a process of calculating the first CSI and modifying the first CSI.
  • the 2 codebooks based operation scheme may be applied to the 2Tx and/or 4Tx antennas system by defining and using the mapping relation between antenna ports while using 2 codebooks for the legacy 8Tx.
  • FIG. 11 is a flowchart for a channel estimating method using a reference signal according to the present invention.
  • a UE may receive a CRS and a CSI-RS from a base station.
  • the UE may correspond to a UE in which a transmission mode (e.g., TM X) for generating and reporting CSI based on the CSI-RS and performing demodulation based on the CRS is configured.
  • a transmission mode e.g., TM X
  • the UE may generate the CSI on a CRS based-channel (e.g., a channel corresponding to the CRS port or a channel estimated using the CRS) based on the CSI on a CSI-RS based-channel (e.g., a channel corresponding to a CSI-RS port or a channel estimated using the CSI-RS) and a mapping relation (e.g., a matrix M in the aforementioned embodiments) between the CRS port and the CSI-RS port.
  • a CRS based-channel e.g., a channel corresponding to the CRS port or a channel estimated using the CRS
  • a mapping relation e.g., a matrix M in the aforementioned embodiments
  • the UE needs to report the CSI on the CRS based-channel to a base station.
  • the UE may directly generate the CSI (e.g., second CSI) on the CRS based-channel without generating the CSI (e.g., first CSI) on the CSI-RS based-channel.
  • the UE may generate the second CSI in a manner of modifying the first CSI in consideration of the mapping relation between the CRS port and the CSI-RS port after generating the first CSI on the CSI-RS based-channel.
  • the UE may report the generated CSI (e.g., second CSI) to the base station.
  • the generated CSI e.g., second CSI
  • the UE may report both the first CSI and the second CSI to the base station. For instance, the UE may report the second CSI to the base station after reporting the first CSI to the base station.
  • the UE may perform data demodulation based on the channel estimated using the CRS.
  • the mapping relation between two or more among the CRS port, the CSI-RS port and a data layer may be defined as what is explained in the aforementioned Formula 3 to 12.
  • a scheme as rank restriction, port restriction and the like may be applied.
  • the UE may generate/calculate the first CSI and/or the second CSI based on an assumption that there does not exist a DMRS (or UE-specific RS).
  • DMRS based-data demodulation or CRS based-data demodulation may be performed according to whether an MBSFN subframe is configured and the UE may obtain relevant information via downlink scheduling information (or a DCI format).
  • the CRS based-demodulation may be performed instead of the DMRS based-demodulation irrespective of whether the MBSFN subframe is configured.
  • the UE reports the first CSI to the base station as it is and may not report the second CSI.
  • the base station calculates a proper precoding matrix for the channel of the CRS port and may inform the UE of the precoding matrix. Since the detailed operation of the base station is duplicated with what is mentioned in the embodiment 2, it is omitted here for clarity.
  • a main entity of downlink transmission is mainly explained by an example of a base station and a main entity of downlink reception is mainly explained by an example of a user equipment, by which a scope of the present invention may be non-limited.
  • a relay becomes the main entity of the downlink transmission to the UE or the relay becomes the main entity of uplink reception from the UE, or in case that the relay becomes the main entity of the uplink transmission to the base station or the relay becomes the main entity of downlink reception from the base station
  • the principle of the present invention explained via various embodiments may be identically applied as well.
  • FIG. 12 is a diagram for a configuration of a preferred embodiment for a user equipment device according to the present invention.
  • a user equipment device 1200 may include a reception module 1210 , a transmission module 1220 , a processor 1230 , a memory 1240 , and a plurality of antennas 1250 .
  • a plurality of the antennas 1250 indicates a user equipment device supporting MIMO transmission and reception.
  • the reception module 1210 may receive various signal, data, and information from external (e.g., base station).
  • the transmission module 1220 may transmit various signals, data, and information to the external (e.g., base station).
  • the processor 1230 may control overall operations of the user equipment device 1200 .
  • the user equipment device 1200 may be configured to perform channel estimation.
  • the processor 1230 may be configured to receive a CRS and a CSI-RS using the reception module 1210 . And, the processor 1230 may be configured to generate CSI on a channel estimated using the CRS based on CSI on a channel estimated using the CSI-RS and a mapping relation between the CRS port and the CSI-RS port. And, the processor 1230 may be configured to report the generated CSI to the base station using the transmission module. And, the processor 1230 may be configured to demodulate data based on the channel estimated using the CRS.
  • the processor 1230 of the user equipment device 1200 performs a function of calculating information received by the user equipment device 1200 , information to be transmitted to the external and the like.
  • the memory 1240 may store the calculated information and the like for a predetermined time and may be replaced with such a configuration element as a buffer (not depicted) or the like.
  • Detail configuration of the aforementioned user equipment device 1200 may be implemented in a manner that the aforementioned items explained in various embodiments of the present invention are independently applied or two or more embodiments are simultaneously applied. For clarity, explanation on the duplicated contents is omitted.
  • a base station device may be configured to transmit the CRS, the CSI-RS and data to the user equipment device 1200 via the transmission module. And, the base station device may be configured to receive the CSI on the CSI-RS based-channel and the CSI on the CRS based-channel, which is generated in consideration of a mapping relation between the CRS port and the CSI-RS port, from the user equipment via the reception module. The base station may provide information on the mapping relation between the CRS port and the CSI-RS port to the UE.
  • the base station receives the CSI on the CSI-RS based-channel from the user equipment via the reception module, determines a precoding matrix (e.g., P2 in Formula 13) compensating for the CRS based-channel and the CSI-RS based-channel, and may inform the user equipment of the precoding matrix via the transmission module.
  • a precoding matrix e.g., P2 in Formula 13
  • Explanation on the user equipment device 1200 in FIG. 12 may be identically applied to a relay node device as an uplink transmission main entity or a downlink reception main entity. And, explanation on the base station may be identically applied to the relay node device as a downlink transmission main entity or an uplink transmission main entity.
  • Embodiments of the present invention may be implemented using various means. For instance, embodiments of the present invention may be implemented using hardware, firmware, software and/or any combinations thereof.
  • a method according to each embodiment of the present invention may be implemented by at least one selected from the group consisting of ASICs (application specific integrated circuits), DSPs (digital signal processors), DSPDs (digital signal processing devices), PLDs (programmable logic devices), FPGAs (field programmable gate arrays), processor, controller, microcontroller, microprocessor and the like.
  • ASICs application specific integrated circuits
  • DSPs digital signal processors
  • DSPDs digital signal processing devices
  • PLDs programmable logic devices
  • FPGAs field programmable gate arrays
  • processor controller, microcontroller, microprocessor and the like.
  • a method according to each embodiment of the present invention may be implemented by modules, procedures, and/or functions for performing the above-explained functions or operations.
  • Software code is stored in a memory unit and is then drivable by a processor.
  • the memory unit is provided within or outside the processor to exchange data with the processor through the various means known in public.

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